Will pulls his hand back in through the gap, clutching the key fob in a white-knuckled fist. Good aim, Piotr, he thinks. He latches the window, turns, and saunters casually out of the kitchen.

Graves is staring at him, a question in his eyes. "Glass of water," Will says. He picks up the laptop. "Are we OK to hook into the network down here?"

The office manager says, "We've come to an agreement. Ms Jonsson says you just need to look at the traffic?"

"That's right," Will says. He plugs the laptop into an Ethernet socket. "Let's take a look."

He boots up PECKSNIFF and punches in a few commands; it's set up to do its thing regardless of what he does, so he makes it look interesting, making minute adjustments to a variety of bogus program settings. By now, Piotr is on his way down to the lobby – Molly had ruled that having him bump into Graves in the same lift twice is an unacceptable risk, so Will had needed to keep them here for a couple of minutes. Just a little longer…

"What are you seeing?" says Graves. "You got anything?"

Five pairs of eyes on him. Will's running the clock down in his head. He purses his lips, shakes his head. Three, two, one… He looks up from the screen.

"Mr Roland, are you running a backup?" he asks.

The executive frowns. "I don't… No, they only run at night."

"Why?" asks Graves.

Will says, "Because it looks like your servers are being backed up to an offsite location. All your data, your user accounts, everything. The transfer's been started in the last ten minutes."

Ercia Jonsson goes very still. Her face is a wax mask. For a second it looks like Alan Roland considers putting a hand out to touch his boss's arm, then draws it away.

There's a moment of silence; when it comes, her voice is a croak. "Stop it."

"Look, I can stop this, but they already got, like, thirty, forty percent of everything you have," says Will. He looks over at Jonsson, frozen in place, and talks fast. "Impossible to tell exactly what. If I stop it now, that's what they've got. I can't get it back, and I can't track them down. They'll know we're on to them.

"But if we let the transfer complete, I can slip them something. A bug. I add it into the files being copied and the first time they try to open it they give away their location. We can find them and stop them before any damage is done." Will sells it as hard as he can. "Ms Jonsson, how much of your data is too much to lose?"

"Any. Any of it," she says. She steps towards Graves, takes him by the elbow.

"You have to find these people. Find them."

Graves says, "We will, Ma'am."

***

Piotr opens the car door and climbs in to the driver's seat. He stows his briefcase in the passenger-side foot well, the drone having been carefully packed away in the boot. He turns to Molly, slouched down in the back seat, and says, "Well?"

Molly takes one earbud out and smiles at him. "They went for it. They're going to try to track us. Hang on." She listens for a second. "Hey, doesn't look like we'll need to track them, anyway. Graves says to contact him at the Buckland Hotel. You know that?"

Piotr starts the engine. "I don't, but I'm a quick study," he says, punching the name into his smartphone's map software. "Let's go and take a look."Molly keeps one ear on the feed from Will's microphone all the way to the hotel, which turns out to be not far from Marble Arch. Graves makes his excuses and leaves a stunned Erica Jonsson and a flustered Alan Roland to wait for developments.

In the lobby, Will says "You'll be the first to know when we find anything," which tells Molly he's managed to slip the key fob back into Jonsson's pocket in the lift; neat and tidy. The way she'd foreseen it in her mind's eye, the bankers would too terrified to be paying attention.

With good reason, she thinks. She idly flicks through some of the files downloaded from the Ballantyne Banham servers, files that reveal exactly how the bank has managed to remain afloat. The falsified accounts. The massive injections of dubious cash. The mysterious foreign investors and vague but lucrative offshore businesses.

In short, the money laundering. Erica Jonsson has been washing billions for organized crime. And that's a dilemma for Molly, because when – or if – she puts this news on the Internet, that stone on the Go board, Jonsson is going to become a target. She's not sure that's the way she wants to play the game.She puts it aside. For now, she's thinking about the next move against Graves.He's clearly a shrewd opponent. She's given him the greatest respect, planned as if he wasn't going to make a mistake. So far, he hasn't disappointed her. Now she needs him to spot the pattern in what's happening, to try to get one up on Damocles; and to give her the name of the man who ordered Danny's death.

They park round the corner from the Buckland. As they go past, Molly gets an impression of old-world English charm; doormen in gold braid and peaked caps, a slightly threadbare red carpet on the front steps. No high-tech security, she thinks. Could be useful.

Piotr feeds the parking meter and wanders over into the lobby. He comes back, pokes his head in through the door, and says "OK, this is what you would call 'an oldie but a goodie'. Are they on their way?"

Molly checks her GPS. The transmitter on the roof of Graves's van is moving steadily towards them. "About ten minutes?"

"That'll do," says Piotr. In the glove compartment is a pack of lemon-yellow stationery. He scrawls a note on a sheet of paper, seals it in an envelope, and hands it to Molly. "Go in, leave this at the desk for Graves, then come back," he says.

Puzzled, Molly takes the envelope and gets out of the car. The doormen give her a sharp look as she goes up the steps and through the revolving doors into the lobby, but they don't stop her. She crosses to the desk, attracts the attention of the receptionist, and says, "Can I leave this for a friend? Lionel Graves – he's staying here?"

He's a cheerful-looking middle-aged man with a magnificent black moustache; his name tag says IMRAN. "Certainly," he says, and plucks the envelope from Molly's fingers.

As he turns, Molly thinks, Ah, I see. The lemon-yellow envelope goes into a numbered pigeonhole behind Imran – number 405, she reads. Easy to spot. "Thanks," she says. She gives Imran a cheery wave and leaves.Piotr's leaning against the car when she gets back, sipping a coffee that he seems to have conjured out of thin air. It's a chilly November day and great clouds of steam rises from the cardboard cup. "405," she says.

"Precisely," he says. "Now: have you heard of a man called Wim Van Eck?"Molly shakes her head. "Nope."

Piotr drains the cup and lobs it gracefully into a nearby bin. "Get in. We are going to need a few things."

They get into the car and Piotr calls the Buckland from his mobile. He asks for his favourite room, one he'd been given on a fictional previous visit, and it turns out room 404 is indeed available, which makes Molly laugh out loud; Piotr shoots her an exasperated look and books himself in for two nights. Then they go shopping.

Wim Van Eck, Piotr explains, was a security researcher who, in the 1980s, had thought of a way to peek at computer screens even when you weren't in the same room. Screens are operated by high frequency electrical signals, which, as a side-effect, turn out to give off radio waves. If you can pick up those waves, you can work your way back to the signals that generated them, and then recreate what was showing on the original screen. "You can read it through walls! It's really quite cool," Piotr tells her.

On Tottenham Court Road they buy themselves an oscilloscope, a signal amplifier, and an antenna that's mercifully rather smaller than the one they'd used to spoof Drake's mobile phone. It all packs neatly into a scuffed second-hand suitcase Molly spots in a charity shop. "That should do it," Piotr says. "I check in, and you can monitor from home."

"Don't worry," says Piotr. He drops her at Marble Arch tube station, parks the car in a garage, and walks off towards the Buckland Hotel, his case full of gadgets in tow.

The next instalment of Root will be available on Wednesday. If you can't wait till then, take the Acenet challenge to see if you have what it takes to join this secret world. Then join the discussion on our Facebook page and test your wits against the top Acenet members